In wireless communication systems such as Global System for Mobile communications (GSM), Wideband Code Division Multiple Access (WCDMA) and Long Term Evolution (LTE), discontinuous reception (DRX) allows the user equipment to save its battery consumption. The user equipment's battery life time is important for the network to ensure that its subscriber's don't have to recharge the battery unnecessarily and are able to access the network services whenever desired. The DRX cycle adjusts the user equipment's radio receiver activity depending on what kind of online service that is currently accessed. The DRX operation is employed not only in idle, or low activity states, but also in connected mode. In principle this allows the network to have considerable control on the overall user equipment power consumption in idle and connected modes.
In low activity states the DRX is used to save the user equipment battery power consumption. In such states the user equipment is able to receive paging or very short packets only at well-defined periodic instances depending upon the actual DRX state. The periodicity of the DRX operation is determined by the DRX cycle, which is set by the network. A typical DRX cycle may range e.g. from 0.1 second to 10 seconds. In both WCDMA and LTE the DRX cycle is user-specific, which means different users in the same cell are individually assigned a DRX cycle. It is initially assigned to the user equipment at the time of registration but later on it can be altered (shortened or extended) any time by the network. Furthermore, the DRX cycle can be assigned by the core network through non access stratum (NAS) procedures using higher layer protocol signalling.
In low activity states, the user equipment autonomously decides when and which cell to reselect. To some extent the user equipment mobility behaviour is controlled by some broadcasted system parameters and performance specification. The cell reselection in the user equipment relies on some downlink measurements. More specifically in order to be able to camp to the correct cell, e.g. best cell in terms of radio conditions, the user equipment regularly performs two important tasks: 1) identification of new neighbour cells, and 2) downlink measurements on the identified neighbour cells. The two tasks are carried out by the user equipment in parallel. Furthermore, the user equipment has to keep track of at least a certain number of cells, e.g. 8 in WCDMA, in terms of their identification and neighbour cell measurements.
In low activity states the user equipment performs cell identification and neighbour cell measurements during the paging occasions or the so-called wake up instances, i.e. the time during which the user equipment wakes up to listen to the expected paging or other relevant information. Generally the wake up instances are very short. e.g. less than 1 ms. This has direct impact on the measurement performance since user equipment is unable to collect sufficient number of measurement samples during a certain time period. More specifically the following aspects of the measurement performance are affected: 1) cell identification delay is extended (e.g. up to several seconds), 2) measurement accuracy of the measurement quantities become worse, 3) physical layer measurement period of the measurement quantities over which desired measurement accuracy is defined. The user equipment is not mandated to wake up only at the paging occasions. However, in practical implementation the user equipment will avoid switching on its receiver as much as possible during the sleep period. In very long DRX cycles (e.g. 5 seconds) the user equipment may wake up few times in between the paging occasions to perform measurements to make sure at least some minimum measurement quality is maintained. The last two aspects (accuracy and measurement period) could be traded to some extent, i.e. shorter measurement period with relatively worse accuracy and vice versa. In e.g. WCDMA all the above measurement performance aspects are worse than those achievable in active or connected mode, where much more intense measurement sampling rate is possible.
On paging reception or arrival of data the user equipment is required to change its state from idle or low activity to higher activity state or directly from idle to the active state. Obviously longer DRX cycle will lead to longer transition from idle to higher activity state, or in other words longer delay in accessing the incoming call or data. For conventional services like speech and classical packet data, the delay may not have severe impact. However, for some advanced services like online gaming the transition should be as fast as possible.
In WCDMA, DRX in active or the so-called Radio Resource Control (RRC) connected mode allows a user equipment to save its battery while staying connected since it wakes up only at periodic instances according to the DRX cycle. The DRX operation in active mode is also employed in LTE. The basic configuration of the DRX cycle and associated parameters is done via RRC signalling in both LTE and WCDMA. But still to some extent the DRX operation is controlled via lower layer signalling directly between the base station and the user equipment. This allows the network to promptly activate and deactivate the DRX operation.
In active or connected mode, the user equipment has to perform measurements to enable handovers. As in case of idle mode the user equipment regularly performs the following two major tasks in active mode: 1) Identification of new neighbouring cells, and 2) downlink measurements on the identified neighbour cells.
The DRX feature implies that the user equipment will mostly collect measurement samples at the wake up instances. Accordingly the measurement requirements in WCDMA have been relaxed in DRX mode. This means there will be much longer cell identification and measurement reporting delay in DRX. For instance the measuring reporting delay will be extended from 200 ms (in continuous reception mode) to around 5-6 seconds in WCDMA in the worst possible DRX scenario, i.e. user equipment only wakes up at the end of the longest possible DRX. The handover should not be delayed to avoid loss of data. Thus the impact on the mobility in active mode is more severe in the idle mode.
One difference between idle and active modes is that in the latter case generally much shorter DRX cycles are used. In LTE the DRX cycle in the order of up to 1 second is envisaged. Nevertheless, the delay in accessing the service compared to the continuous reception scenario is unavoidable. For some services like gaming and voice over IP the delay should be minimized. Another issue is that, due to DRX and especially in case of longer DRX, the network may not be able to fully exploit the characteristics of channel dependent scheduling. This may cause some throughput degradation compared to the continuous reception scenario.
In the past the main objective of the user equipment was to access voice and later on data services, which are offered by the network operator to its subscribers. These services will be referred to as online services. Traditional cell phones and even presently the low end user equipments are designed mainly to access online services. However the present and especially the future user equipments are incorporating at least two major evolutionary set of features: 1) offline, i.e. local services and 2) multiple set of online service technologies on the same terminal. Cell phone technology has dramatically evolved in terms of providing local services and features whose existence on a particular user equipment and accessed by the subscriber remain transparent to the operator because they are accessed without network's intervention. Well known examples of local services are music such as e.g. MP3-players, digital cameras, radio, word processors, advanced calculators, offline games, etc. The traditional conception of a user equipment is being transformed to a full scale computer. Common categories of user equipments are personal digital assistants, smartphones, pocket-computers, palm computers, etc. Another major step is that the same user equipment could support multiple technologies. Typical examples are combination of:                TDD/FDD (Time Division Duplex/Frequency Division Duplex) WCDMA for unicast services and DVB-H for broadcast services        TDD/FDD WCDMA for unicast services and FDD/TDD MBSFN (on different carriers)        TDD/FDD LTE for unicast/broadcast and DVB-H for broadcast servicesFirstly it is not likely that all operators offer services related to all categories and combination of technologies. Secondly, even if an operator offers several of these services, it may still not be possible for each individual network (especially the lower protocol layers) to be aware of subscriber's activity and usage of other possible technologies, which are available on its user equipment. Additionally a subscriber due to economic or any other reason may choose not to access all set of services from the same service provider. Lastly the subscriber could access the services offered by different technologies independently.        
The advanced user equipment bearing multiple local services and technologies are expensive. Therefore subscribers would expect overall better overall performance from all aspects, e.g. mobility, local services, etc. Further, the subscriber is likely to use its user equipment for multiple tasks on a more regular basis. This approach but will drain user equipment battery due to its frequent activation. It is also likely that subscriber uses the local features more often when moving around rather than when staying at home. For instance the user may prefer to use the user equipment to play music or take photos when driving a car or during a casual stroll, but instead prefer to use the standalone music players or cameras for example when attending a party. Evidently during mobility the level of accuracy and delays associated with the synchronization, measurements, etc, performed by the user equipment become critical.
In WO 00/22837 a variable sleep mode for mobile stations is presented where the sleep cycle of the mobile station may be optimally varied depending on one or more conditions relating to the mobile station's operation. In WO 00/22837 an improved service quality/delay leads to increased battery consumption. The variable sleep mode capabilities in WO 00/22837 permits optimization of the tradeoff between battery consumption and service quality/delay in accordance with the individual objectives and/or conditions of a particular user/mobile station.